Refrigerating machine and control method thereof

ABSTRACT

A refrigerating machine which is equipped with: a turbocompressor 2 that compresses a refrigerant; a condenser 3 that condenses the refrigerant compressed by the turbocompressor 2; an intermediate cooler 4 that is a plate heat exchanger which performs heat exchange between the liquid refrigerant introduced from the condenser 3 and the two-phase refrigerant obtained by expanding, with a sub-expansion valve 13, part of the liquid refrigerant introduced from the condenser 3; a main expansion valve 5 that expands the liquid refrigerant introduced from the intermediate cooler 4; and an evaporator 7 that evaporates the refrigerant introduced from the main expansion valve 5. The plate heat exchanger includes 80 or more laminated plates, the width of which is 100-400 mm and the height of which is 300-1000 mm.

TECHNICAL FIELD

The present invention relates to a refrigerator having an economizer which is a plate type heat exchanger and a control method thereof.

BACKGROUND ART

For example, as described in PTL 1, in a two-stage compression subcooler one-stage expansion cycle, an economizer is a plate type heat exchanger. Accordingly, compared to a gas-liquid separation type economizer used in a two-stage compression subcooler two-stage expansion cycle, a refrigerant charge amount can be reduced.

CITATION LIST Patent Literature

[PTL 1] Japanese Unexamined Patent Application Publication No. 2012-77971 ([0034], FIG. 1)

SUMMARY OF INVENTION Technical Problem

However, in a case where a temperature of cooling water is low and a refrigerant circulation amount is large, there is a problem that a differential pressure across expansion valve (=condensation pressure evaporation pressure−pressure loss of economizer) decreases, and there is a problem that an expansion valve opening degree becomes too large and cannot be controlled. As a countermeasure against this, it is conceivable to increase a diameter of an expansion valve. However, a flow rate adjustment amount with the minimum opening degree change increases, and thus, there is a problem that accuracy of an expansion valve control deteriorates.

As another countermeasure, it is conceivable to increase the number of stacked economizers and increase a cross-sectional area of the entire flow path so as to reduce the pressure loss. However, even if the pressure loss is reduced by increasing the number of the stacked economizers, a resistance decreases when a two-phase refrigerant passing through a sub-expansion valve is distributed to each flow path, and thus, a deviation of a refrigerant distribution occurs. In this case, a heat transfer area of the economizer cannot be effectively used, and performance of a refrigerator deteriorates. In addition, a carry-over occurs in which the two-phase refrigerant flows into an intermediate intake port of a compressor in a state where the two-phase refrigerant is not fully gasified.

The present invention is made in consideration of the above-described circumstances, and an object thereof is to provide a refrigerator capable of being appropriately operated against an increase of a refrigerant circulation amount generated in a case where a plate type heat exchanger is used as the economizer and a control method thereof.

Solution to Problem

In order to achieve the object, a refrigerator and a control method thereof according to the present invention adopts the following means.

That is, according to an aspect of the present invention, there is provided a refrigerator including: a compressor which compresses a refrigerant; a condenser which condenses the refrigerant compressed by the compressor; an economizer which is a plate type heat exchanger which performs heat exchange between a liquid refrigerant introduced from the condenser and a two-phase refrigerant obtained by expanding a portion of the liquid refrigerant introduced from the condenser by a sub-expansion valve; a main expansion valve which expands the liquid refrigerant introduced from the economizer; and an evaporator which expands the refrigerant introduced from the main expansion valve, in which the plate type heat exchanger is configured such that a width of a plate is 100 mm or more and 400 mm or less, a height of the plate is 300 mm or more and 1,000 mm or less, and the number of stacked plates is 80 or more.

The plate type heat exchanger is used as the economizer, the width of the stacked plates is 100 mm or more and 400 mm or less, the height of the stacked plates is 300 mm or more and 1,000 mm or less, and the number of the stacked plates is 80 or more. Accordingly, a pressure loss of the economizer can be 100 kPa or more, preferably, can be 150 kPa or more and 200 kPa or less. Therefore, even when a refrigerant circulation amount increases, a predetermined pressure loss can be secured, and thus, a refrigerant distribution in the economizer which is the plate type heat exchanger is appropriately performed, and it is possible to operate a refrigerator without damaging performance of the refrigerator.

As a refrigerant, HFC-134a is appropriately used, or HFO-1234ze(E), HFO-1233zd(E), or HFO-1233zd(Z) may be used.

In addition, according to another aspect of the present invention, there is provided a refrigerator including: a compressor which compresses a refrigerant; a condenser which condenses the refrigerant compressed by the compressor; an economizer which is a plate type heat exchanger which performs heat exchange between a liquid refrigerant introduced from the condenser and a two-phase refrigerant obtained by expanding a portion of the liquid refrigerant introduced from the condenser by a sub-expansion valve; a main expansion valve which expands the liquid refrigerant introduced from the economizer; an evaporator which evaporates the refrigerant introduced from the main expansion valve; a bypass path which bypasses the economizer and through which the liquid refrigerant from the condenser is introduced to an upstream side of the main expansion valve; a bypass valve which is provided in the bypass path; and a controller which controls an opening degree of the bypass valve.

The bypass valve is opened by a command of the controller, and a flow rate of the refrigerant flowing through the bypass path increases. Accordingly, it is possible to decrease a flow rate of the liquid refrigerant which flows into the economizer. Therefore, even in a case where the refrigerant circulation amount increases, it is possible to prevent the liquid refrigerant from excessively flowing into the economizer. Accordingly, it is possible to suppress occurrence of a failure of the refrigerant distribution in the economizer which is the plate type heat exchanger.

In addition, according to still another aspect of the present invention, there is provided a refrigerator including: a compressor which compresses a refrigerant; a condenser which condenses the refrigerant compressed by the compressor; an economizer which is a plate type heat exchanger which performs heat exchange between a liquid refrigerant introduced from the condenser and a two-phase refrigerant obtained by expanding a portion of the liquid refrigerant introduced from the condenser by a sub-expansion valve; a main expansion valve which expands the liquid refrigerant introduced from the economizer; an evaporator which evaporates the refrigerant introduced from the main expansion valve; a bypass path which bypasses the economizer and through which the liquid refrigerant from the condenser is introduced to a cooled-medium inlet side of the evaporator; a bypass valve which is provided in the bypass path; and a controller which controls an opening degree of the bypass valve.

The bypass valve is opened by a command of the controller, and a flow rate of the refrigerant flowing through the bypass path increases. Accordingly, it is possible to decrease a flow rate of the liquid refrigerant which flows into the economizer. Therefore, even in a case where the refrigerant circulation amount increases, it is possible to prevent the liquid refrigerant from excessively flowing into the economizer. Accordingly, it is possible to suppress occurrence of a failure of the refrigerant distribution in the economizer which is the plate type heat exchanger.

In addition, the main expansion valve can be bypassed, and thus, it is not necessary to adopt an expansion valve having a large diameter in anticipation of an increase of the refrigerant circulation amount, and there is no possibility that control accuracy of the expansion valve deteriorates.

In addition, the liquid refrigerant is introduced to the cooled-medium (for example, cold water) inlet side of the evaporator via the bypass path. Accordingly, the refrigerant can be introduced to the cooled-medium inlet side which is a region in which a heat exchange amount is large, the refrigerant is evaporated, and thus, dry-out easily occurs. Therefore, the dry-out in this region is suppressed, and it is possible to improve a heat transfer coefficient in the evaporator.

In addition, in the refrigerator according to the aspects of the present invention, in a case where a difference between a pressure in the condenser and a pressure in the evaporator is equal or less than a predetermined value or an opening degree of the main expansion valve is equal to or more than a predetermined value, the controller increases the opening degree of the bypass valve.

If the difference between the pressure in the condenser and the pressure in the evaporator is equal to or less than the predetermined value or the opening degree of the main expansion valve is equal to or more than the predetermined value, it is determined that the refrigerant circulation amount is excessive, and thus, the opening degree of the bypass valve increases. Accordingly, it is possible to suppress occurrence of the failure of the refrigerant distribution in the economizer which is the plate type heat exchanger.

In addition, according to still aspect of the present invention, there is provided a control method of a refrigerator, the refrigerator includes a compressor which compresses a refrigerant, a condenser which condenses the refrigerant compressed by the compressor, an economizer which is a plate type heat exchanger which performs heat exchange between a liquid refrigerant introduced from the condenser and a two-phase refrigerant obtained by expanding a portion of the liquid refrigerant introduced from the condenser by a sub-expansion valve, a main expansion valve which expands the liquid refrigerant introduced from the economizer, an evaporator which evaporates the refrigerant introduced from the main expansion valve, a bypass path which bypasses the economizer and introduces the liquid refrigerant from the condenser to an upstream side of the main expansion valve, and a bypass valve which is provided in the bypass path, the control method including: increasing the opening degree of the bypass valve in a case where a difference between a pressure in the condenser and a pressure in the evaporator is equal or less than a predetermined value or an opening degree of the main expansion valve is equal to or more than a predetermined value.

The bypass valve is opened and a flow rate of the refrigerant flowing through the bypass path increases. Accordingly, it is possible to decrease a flow rate of the liquid refrigerant which flows into the economizer. Therefore, even in a case where the refrigerant circulation amount increases, it is possible to prevent the liquid refrigerant from excessively flowing into the economizer. Accordingly, it is possible to suppress occurrence of a failure of the refrigerant distribution in the economizer which is the plate type heat exchanger.

In addition, according to still aspect of the present invention, there is provided a control method of a refrigerator, the refrigerator includes a compressor which compresses a refrigerant, a condenser which condenses the refrigerant compressed by the compressor, an economizer which is a plate type heat exchanger which performs heat exchange between a liquid refrigerant introduced from the condenser and a two-phase refrigerant obtained by expanding a portion of the liquid refrigerant introduced from the condenser by a sub-expansion valve, a main expansion valve which expands the liquid refrigerant introduced from the economizer, an evaporator which evaporates the refrigerant introduced from the main expansion valve, a bypass path which bypasses the economizer and through which the liquid refrigerant from the condenser is introduced to a cooled-medium inlet side of the evaporator, and a bypass valve which is provided in the bypass path, the control method including: increasing the opening degree of the bypass valve in a case where a difference between a pressure in the condenser and a pressure in the evaporator is equal or less than a predetermined value or an opening degree of the main expansion valve is equal to or more than a predetermined value.

The bypass valve is opened and a flow rate of the refrigerant flowing through the bypass path increases. Accordingly, it is possible to decrease a flow rate of the liquid refrigerant which flows into the economizer. Therefore, even in a case where the refrigerant circulation amount increases, it is possible to prevent the liquid refrigerant from excessively flowing into the economizer. Accordingly, it is possible to suppress occurrence of a failure of the refrigerant distribution in the economizer which is the plate type heat exchanger.

In addition, the main expansion valve can be bypassed, and thus, it is not necessary to adopt an expansion valve having a large diameter in anticipation of an increase of the refrigerant circulation amount, and there is no possibility that control accuracy of the expansion valve deteriorates.

In addition, the liquid refrigerant is introduced to the cooled-medium (for example, cold water) inlet side of the evaporator via the bypass path. Accordingly, the refrigerant can be introduced to the cooled-medium inlet side which is a region in which the heat exchange amount is large, the refrigerant is evaporated, and thus, dry-out easily occurs. Therefore, the dry-out in this region is suppressed, and it is possible to improve a heat transfer coefficient in the evaporator.

Advantageous Effects of Invention

By appropriately selecting the width, the height, and the number of the stacked plates, it is possible to secure a predetermined pressure loss even when the refrigerant circulation amount increases. Accordingly, the refrigerant distribution in the economizer which is the plate type heat exchanger is appropriately performed, and it is possible to operate a refrigerator without damaging performance of the refrigerator.

Even when the refrigerant circulation amount increases, the flow rate of the refrigerant which flows through the bypass path which bypasses the economizer increases. Accordingly, it is possible to decrease the flow rate of the liquid refrigerant flowing into the economizer, and thus, it is possible to suppress occurrence of a failure of the refrigerant distribution in the economizer which is the plate type heat exchanger.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration diagram showing a turbo refrigerator according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional diagram showing a schematic configuration of an economizer of FIG. 1.

FIG. 3 is a diagram showing a result of thermography of an economizer according to the first embodiment.

FIG. 4 is a diagram showing a result of thermography of an economizer according to a reference example.

FIG. 5 is a schematic configuration diagram showing a turbo refrigerator according to a second embodiment of the present invention.

FIG. 6 is a schematic configuration diagram showing a turbo refrigerator according to a third embodiment of the present invention.

FIG. 7 is a longitudinal sectional diagram schematically showing an evaporator of FIG. 6.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

First Embodiment

Hereinafter, a first embodiment of the present invention will be described.

As shown in FIG. 1, a turbo refrigerator (refrigerator) 1 includes a turbo compressor (compressor) 2, a condenser 3, an economizer 4, a main expansion valve 5, an evaporator 7, and a controller (not shown).

The turbo compressor 2 is a centrifugal compressor which is driven by an inverter motor 9 and includes an intermediate intake port 2C provided between a first impeller (not shown) and a second impeller (not shown) in addition to an intake port 2A and a discharge port 2B. A low-pressure gas refrigerant sucked from the intake port 2A is compressed in two stages by rotations of the first impeller and the second impeller, and the compressed high-pressure gas refrigerant is discharged from the discharge port 2B.

As a refrigerant, HFC-134a is used. However, HFO-1234ze(E), HFO-1233zd(E), or HFO-1233zd(Z) may be used.

The high-pressure gas refrigerant discharged from the discharge port 2B of the turbo compressor 2 is introduced to an oil mist separation tank 10, and oil in the refrigerant is centrifugally separated. The high-pressure cooling gas from which the oil is centrifugally separated is introduced from the oil mist separation tank 10 to the condenser 3.

The condenser 3 is a shell and tube type heat exchanger and performs heat exchange between the high-pressure gas refrigerant supplied via the oil mist separation tank 10 from the turbo compressor 2 and cooling water which circulates a cooling water circuit 11, and thus, the high-pressure cooling gas is condensed and liquefied. The cooling water circuit 11 is connected to a cooling tower (not shown) and the cooling water is cooled to a predetermined temperature by the cooling tower. In addition, preferably, the flow of the cooling water supplied by a cooling water pump 12 and the flow of the high-pressure gas refrigerant are made to flow countercurrently. Moreover, as the condenser 3, a plate type heat exchanger may be used.

The economizer 4 is the plate type heat exchanger which performs heat exchange between a liquid refrigerant which flows through a main circuit of a refrigeration cycle 8 and is introduced from the condenser 3 and a two-phase refrigerant which branches off from the main circuit and is decompressed by the sub-expansion valve 13 and supercools the liquid refrigerant flowing through the main circuit by evaporation latent heat of the refrigerant. In addition, a gas circuit 14 through which a gas refrigerant (intermediate-pressure refrigerant) which is evaporated by supercooling the liquid refrigerant is injected into a compressed refrigerant having an intermediate pressure from the intermediate intake port 2C of the turbo compressor 2 is connected to the economizer 4.

The refrigerant supercooled via the economizer 4 passes through the main expansion valve 5 to be expanded and is supplied to the evaporator 7. The evaporator 7 is the shell and tube type heat exchanger and performs heat exchange between the refrigerant introduced from the main expansion valve 5 and the cold water (cooled medium) which circulates via a cold water circuit 15, evaporates the refrigerant, and cools the cold water by the evaporation latent heat. In addition, preferably, the flow of the cold water supplied by the cold water pump 16 and the flow of the refrigerant are made to flow countercurrently. Moreover, as the evaporator 7, a plate type heat exchanger may be used.

In addition, the refrigeration cycle 8 includes a hot gas bypass circuit 17 which bypasses a portion of the high-pressure gas refrigerant in which the oil is separated by the oil mist separation tank 10 from between the condenser 3 and the turbo compressor 2. A hot gas bypass valve 18 is provided in the hot gas bypass circuit 17, and the hot gas bypass valve 18 adjusts a flow rate of the high-pressure gas refrigerant introduced from the hot gas bypass circuit 17 to the turbo compressor 2.

As measuring means for measuring temperatures or pressures of the refrigerant, the cooling water, and the cold water, pressure gauges 41, 42, and 43 and thermometers 31, 32, and 33 are provided in the intake port 2A of the turbo compressor 2, the discharge port 2B, and the intermediate intake port 2C, and thermometers 35, 36, 37, and 38 are respectively provided in an inlet and an outlet of the cooling water circuit 11 and an inlet and an outlet of the cold water circuit 15, and the thermometer 34 is provided in the inlet of the main expansion valve 5.

The turbo refrigerator 1 is controlled by the controller (not shown). For example, the controller includes a Central Processing Unit (CPU), a Random Access Memory (RAM), a Read Only Memory (ROM), a computer readable storage medium, or the like. In addition, for example, a series of processing for realizing various functions is stored in the storage medium or the like as a program form, and the CPU reads the program to a RAM or the like and executes information processing/calculation processing to realize the various functions. The program may be installed in the ROM or other storage mediums in advance, may be supplied in a form stored in a computer readable storage medium, or may be distributed via wired or wireless communication means. The computer readable storage medium is a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like.

FIG. 2 shows a schematic configuration of the economizer 4. The economizer 4 is the plate type heat exchanger in which the plurality of stacked plates 40 are stacked to form a plurality of flow paths adjacent to each other in parallel. In addition, only six flow paths 42 a and 42 b are shown in FIG. 2. However, this is merely an example, and actually, 80 flow paths or more may be formed.

The flow paths 42 a of the liquid refrigerant which are introduced from the condenser 3 (indicated by “CON” in the drawing) and the flow paths 42 b of the two-phase refrigerant which branch from the condenser 3 and are introduced after passing through the sub-expansion valve are alternately provided and are made to flow countercurrently.

The liquid refrigerant from the condenser 3 passes through the flow paths 42 a from the upper side in the drawing toward the lower side in the drawing to pass through the economizer 4. The liquid refrigerant which has flowed through the economizer 4 is throttled by the main expansion valve 5 and, thereafter, is introduced to the evaporator 7 (indicated by “EVA” in the drawing).

A portion of the liquid refrigerant branching from the condenser 3 is throttled by the sub-expansion valve 13 so as to be the two-phase refrigerant, and thereafter, flows into each of the flow paths 42 b of the economizer 4, and flows from the upper side in the drawing to the lower side. A distributor 44 which applies a predetermined pressure loss is provided on the upstream side of each of the flow paths 42 b. The two-phase refrigerant can be uniformly distributed to each of the flow paths 42 b by the distributor 44. The gas refrigerant, which is changed from the two-phase refrigerant to the gas refrigerant while passing through the economizer 4, flows from the intermediate intake port 2C of the turbo compressor 2 (indicated by “COMP” in the drawing).

In this way, the liquid refrigerant which is introduced from the condenser 3 and flows through the flow paths 42 a from the upper side to the lower side in the drawing is cooled by the evaporation latent heat of the adjacent two-phase refrigerant so as to be a supercooled refrigerant, and the two-phase refrigerant which is introduced from the sub-expansion valve 13 and flows through the flow path 42 b from the lower side to the upper side in FIG. 1 acquires the evaporation latent heat from the adjacent liquid refrigerant and is changed to the gas refrigerant.

The width of the stacked plates 40 is 100 mm or more and 400 mm or less, the height of the stacked plates 40 is 300 mm or more and 1000 mm or less, and the number of the stacked plates 40 is 80 or more and 400 or less. Accordingly, the pressure loss of the economizer 4 can be 100 kPa or more, and, preferably, can be 150 kPa or more and 200 kPa or less. In addition, it is possible to suppress the failure in the refrigerant distribution of the flow path 42 b of the two-phase refrigerant.

The pressure loss of the economizer 4 which is the plate type heat exchanger is adjusted by increasing or decreasing the number of the stacked plates 40. Specifically, a total cross-sectional area of the flow path is increased by increasing the number of the stacked plates, a flow rate decreases, and thus, the pressure loss decreases. In addition, the total cross-sectional area of the flow path is decreased by decreasing the number of stacked plates, the flow rate increases, and thus, the pressure loss increases.

FIGS. 3 and 4 show a state of the refrigerant distribution in the economizer 4.

FIG. 3 shows the economizer 4 according to the present embodiment, and the number of the stacked plates is 86. As the refrigerant, HFC-134a is used. FIG. 3 shows a result of thermography when the economizer 4 is viewed from the front surface as shown in FIG. 2. That is, a right-left direction in the drawings is a stacking direction, the two-phase refrigerant flow from the lower side toward the upper side, and the liquid refrigerant flows from the upper side toward the lower side. It can be understood from FIG. 3 that a temperature difference in the right-left direction is not large. This means that the refrigerant distribution is good. In the case of FIG. 3, the pressure loss is 100 kPa or more.

Meanwhile, FIG. 4 is a reference example and shows the result of the thermography similar to FIG. 3. However, FIG. 4 is different from FIG. 3 in that the number of the stacked plates is 212. It can be understood from FIG. 4 that the temperature difference in the right-left direction (stacking direction) is large and the refrigerant distribution is not good. In the case of FIG. 4, the pressure loss is 10 to 20 kPa. In this way, if the number of the stacked plates increases according to the increase of the refrigerant circulation amount, the pressure loss in the economizer decreases, and thus, it can be understood that the failure in the refrigerant distribution occurs.

As described above, according to the present embodiment, the following effects are exerted.

The plate type heat exchanger is used as the economizer 4, the width of the stacked plates 40 is 100 mm or more and 400 mm or less, the height of the stacked plates 40 is 300 mm or more and 1,000 mm or less, and the number of the stacked plates 40 is 80 or more. Accordingly, the pressure loss of the economizer 4 can be 100 kPa or more, preferably, can be 150 kPa or more and 200 kPa or less. Therefore, even when the refrigerant circulation amount increases, a predetermined pressure loss can be secured, and thus, a refrigerant distribution in the economizer 4 which is the plate type heat exchanger is appropriately performed, and it is possible to operate a refrigerator without damaging performance of the refrigerator.

Second Embodiment

Next, a second embodiment of the present invention will be described with reference to FIG. 5.

The present embodiment is different from the first embodiment in that a bypass path is provided, and other portions are similar to each other. Accordingly, the same reference numerals are assigned to the same configurations, and descriptions thereof are omitted.

As shown in FIG. 5, a bypass path 50, which bypasses the economizer 4 and through which the liquid refrigerant from the condenser 3 is introduced to the upstream side of the main expansion valve 5, is provided. An upstream end of the bypass path 50 is provided on a downstream side of a branch point A from which branches to the sub-expansion valve 13.

In addition, a bypass valve 52 is provided in the bypass path 50. As the bypass valve 52, an electrical ball valve capable of adjusting an opening degree is used. However, a solenoid valve which is simply opened or closed may be used. A command of the opening degree of the bypass valve 52 is performed by the controller (not shown). In a case where a difference between a pressure in the condenser 3 and a pressure in the evaporator 7 is equal to or less than a predetermined value, or in a case where an opening degree of the main expansion valve 5 is equal or more than a predetermined value, the controller determines that the refrigerant circulation amount is excessive, and the controller increases the opening degree of the bypass valve 52.

In this way, according to the present embodiment, the bypass valve 52 is opened by the command of the controller to increase the flow rate of the refrigerant flowing through the bypass path 50. Accordingly, it is possible to decrease the flow rate of the liquid refrigerant flowing into the economizer 4. Accordingly, even in a case where the refrigerant circulation amount increases, it is possible to prevent the liquid refrigerant from excessively flowing into the economizer 4. Accordingly, it is possible to suppress occurrence of a failure of the refrigerant distribution in the economizer 4 which is the plate type heat exchanger.

In addition, the plate type heat exchanger having the configuration shown in the first embodiment may not be used as the economizer 4. That is, an economizer may be used in which the pressure loss is adjusted such that a desired refrigerant distribution is performed on the flow rate of the refrigerant which flows into the economizer 4 when the liquid refrigerant is bypassed through the bypass path 50.

Third Embodiment

Next, a third embodiment of the present invention will be described with reference to FIGS. 6 and 7.

The present embodiment is different from the first embodiment in that the bypass path is provided, and other portions are similar to each other. Accordingly, the same reference numerals are assigned to the same configurations, and descriptions thereof are omitted.

As shown in FIG. 6, a bypass path 60, which bypasses the economizer 4 and through which the liquid refrigerant from the condenser 3 is introduced to the cold water (cooled-medium) inlet side of the evaporator 7, is provided. An upstream end of the bypass path 60 is provided on a downstream side of a branch point A from which branches to the sub-expansion valve 13.

In addition, a bypass valve 62 is provided in the bypass path 60. As the bypass valve 62, an electrical ball valve capable of adjusting an opening degree is used. However, a solenoid valve which is simply opened or closed may be used. A command of the opening degree of the bypass valve 62 is performed by the controller (not shown). In a case where the difference between the pressure in the condenser 3 and the pressure in the evaporator 7 is equal to or less than a predetermined value, or in a case where the opening degree of the main expansion valve 5 is equal or more than a predetermined value, the controller determines that the refrigerant circulation amount is excessive, and the controller increases the opening degree of the bypass valve 62.

FIG. 7 shows a schematic configuration of the evaporator 7. The evaporator 7 is a shell and tube type evaporator and a cylindrical container which has an approximately circular cross section and a horizontal axis line. Water chambers to which the cold water is introduced are provided on both end portions of the evaporator 7, and a space which is interposed between the water chambers 45 and 46 becomes an evaporation chamber 47 in which the refrigerant introduced from the economizer 4 exists. Pipe plates 48 are partitioned between the water chambers 45 and 46 and the evaporation chamber 47.

A plurality of heat transfer pipe 49 are connected to each other between the water chambers 45 and 46. The heat transfer pipes 49 configures the plurality of pipe groups (not shown). For example, a liquid distribution structure 68 which is a porous plate for distributing the two-phase refrigerant flowing into the evaporator 7 is provided below the heat transfer pipe 49.

The cold water flowing from one water chamber 45 is returned to the other water chamber 46 through each heat transfer pipe 49, and thereafter, is returned to the water chamber 45 and is introduced to an external load. Accordingly, in this case, one water chamber 45 partitions a chamber for the cold water inlet and a chamber for a cold water outlet.

A refrigerant pipe 53 into which the refrigerant introduced via the main expansion valve 5 from the economizer 4 is introduced is connected to an approximately center position in the horizontal axis line below the evaporator 7. A suction pipe 64 through which the refrigerant gas evaporated in the evaporator 7 is introduced to the intake port 2A of the turbo compressor 2 is connected to an upper portion of the evaporator 7. For example, a gas-liquid separation structure 66 which is a porous plate so as to separate a gas and a liquid is provided in the vicinity of an upstream side of a position at which the suction pipe 64 is connected. A hot gas bypass pipe 65 is connected to an end portion of an upper portion of the evaporator 7.

In addition, the bypass path 60 is connected to the cold water inlet side (the left side in the drawing) from the center position in a horizontal axial direction of the evaporator 7. Accordingly, the refrigerant passing through the bypass valve 62 is introduced to the vicinity of the heat transfer pipe 49 through which the cold water on the cold water inlet side of the evaporator 7 flows.

In this way, according to the present embodiment, the bypass valve 62 is opened by the command of the controller to increase the flow rate of the refrigerant flowing through the bypass path 60. Accordingly, it is possible to decrease the flow rate of the liquid refrigerant flowing into the economizer 4. Accordingly, even in a case where the refrigerant circulation amount increases, it is possible to prevent the liquid refrigerant from excessively flowing into the economizer 4. Accordingly, it is possible to suppress occurrence of a failure of the refrigerant distribution in the economizer 4 which is the plate type heat exchanger.

In addition, the main expansion valve 5 can be bypassed, and thus, it is not necessary to adopt an expansion valve having a large diameter in anticipation of an increase of the refrigerant circulation amount, and there is no possibility that control accuracy of the expansion valve deteriorates.

In addition, the refrigerant is introduced to the inlet side of the cold water of the evaporator 7 via the bypass path 60. Accordingly, the refrigerant can be introduced to the inlet side of the cold water which is a region in which the heat exchange amount is large, the refrigerant is evaporated, and thus, dry-out easily occurs. Therefore, the dry-out in this region is suppressed, and it is possible to improve a heat transfer coefficient in the evaporator.

In addition, the plate type heat exchanger having the configuration shown in the first embodiment may not be used as the economizer 4. That is, an economizer may be used in which the pressure loss is adjusted such that a desired refrigerant distribution is performed on the flow rate of the refrigerant which flows into the economizer 4 when the liquid refrigerant is bypassed through the bypass path 60. REFERENCE SIGNS LIST

1: turbo refrigerator (refrigerator)

2: turbo compressor (compressor)

2A: intake port

2B: discharge port

2C: intermediate intake port

3: condenser

4: economizer

5: main expansion valve

7: evaporator

13: sub-expansion valve

40: stacked plate

50, 60: bypass path

52, 62: bypass valve 

1. A refrigerator comprising: a compressor which compresses a refrigerant; a condenser which condenses the refrigerant compressed by the compressor; an economizer which is a plate type heat exchanger which performs heat exchange between a liquid refrigerant introduced from the condenser and a two-phase refrigerant obtained by expanding a portion of the liquid refrigerant introduced from the condenser by a sub-expansion valve; a main expansion valve which expands the liquid refrigerant introduced from the economizer; and an evaporator which evaporates the refrigerant introduced from the main expansion valve, wherein the plate type heat exchanger is configured such that a width of a plate is 100 mm or more and 400 mm or less, a height of the plate is 300 mm or more and 1,000 mm or less, and the number of stacked plates is 80 or more.
 2. A refrigerator comprising: a compressor which compresses a refrigerant; a condenser which condenses the refrigerant compressed by the compressor; an economizer which is a plate type heat exchanger which performs heat exchange between a liquid refrigerant introduced from the condenser and a two-phase refrigerant obtained by expanding a portion of the liquid refrigerant introduced from the condenser by a sub-expansion valve; a main expansion valve which expands the liquid refrigerant introduced from the economizer; an evaporator which evaporates the refrigerant introduced from the main expansion valve; a bypass path which bypasses the economizer and through which the liquid refrigerant from the condenser is introduced to an upstream side of the main expansion valve; a bypass valve which is provided in the bypass path; and a controller which controls an opening degree of the bypass valve.
 3. A refrigerator comprising: a compressor which compresses a refrigerant; a condenser which condenses the refrigerant compressed by the compressor; an economizer which is a plate type heat exchanger which performs heat exchange between a liquid refrigerant introduced from the condenser and a two-phase refrigerant obtained by expanding a portion of the liquid refrigerant introduced from the condenser by a sub-expansion valve; a main expansion valve which expands the liquid refrigerant introduced from the economizer; an evaporator which evaporates the refrigerant introduced from the main expansion valve; a bypass path which bypasses the economizer and through which the liquid refrigerant from the condenser is introduced to a cooled-medium inlet side of the evaporator; a bypass valve which is provided in the bypass path; and a controller which controls an opening degree of the bypass valve.
 4. The refrigerator according to claim 2, wherein in a case where a difference between a pressure in the condenser and a pressure in the evaporator is equal or less than a predetermined value or an opening degree of the main expansion valve is equal to or more than a predetermined value, the controller increases the opening degree of the bypass valve.
 5. A control method of a refrigerator, the refrigerator includes a compressor which compresses a refrigerant, a condenser which condenses the refrigerant compressed by the compressor, an economizer which is a plate type heat exchanger which performs heat exchange between a liquid refrigerant introduced from the condenser and a two-phase refrigerant obtained by expanding a portion of the liquid refrigerant introduced from the condenser by a sub-expansion valve, a main expansion valve which expands the liquid refrigerant introduced from the economizer, an evaporator which evaporates the refrigerant introduced from the main expansion valve, a bypass path which bypasses the economizer and through which the liquid refrigerant from the condenser is introduced to an upstream side of the main expansion valve, and a bypass valve which is provided in the bypass path, the control method comprising: increasing the opening degree of the bypass valve in a case where a difference between a pressure in the condenser and a pressure in the evaporator is equal or less than a predetermined value or an opening degree of the main expansion valve is equal to or more than a predetermined value.
 6. A control method of a refrigerator, the refrigerator includes a compressor which compresses a refrigerant, a condenser which condenses the refrigerant compressed by the compressor, an economizer which is a plate type heat exchanger which performs heat exchange between a liquid refrigerant introduced from the condenser and a two-phase refrigerant obtained by expanding a portion of the liquid refrigerant introduced from the condenser by a sub-expansion valve, a main expansion valve which expands the liquid refrigerant introduced from the economizer, an evaporator which evaporates the refrigerant introduced from the main expansion valve, a bypass path which bypasses the economizer and through which the liquid refrigerant from the condenser is introduced to a cooled-medium inlet side of the evaporator, and a bypass valve which is provided in the bypass path, the control method comprising: increasing the opening degree of the bypass valve in a case where a difference between a pressure in the condenser and a pressure in the evaporator is equal or less than a predetermined value or an opening degree of the main expansion valve is equal to or more than a predetermined value.
 7. The refrigerator according to claim 3, wherein in a case where a difference between a pressure in the condenser and a pressure in the evaporator is equal or less than a predetermined value or an opening degree of the main expansion valve is equal to or more than a predetermined value, the controller increases the opening degree of the bypass valve. 